Officers arrest a demonstrator at a Wednesday protest in Brooklyn against the shooting of Kimani Gray.Photo: Getty Images

Mahnefah Gray, the sister of Kimani Gray, was among those charged during Wednesday’s protest. (Robert Mecea)

A police officer was smashed in the face with a brick and 50 people were arrested as unrest over a teenager shot dead by cops continued to plague a Brooklyn neighborhood last night.

For the second time this week, swarms of youths roamed the streets of East Flatbush armed with bottles and bricks. One of those arrested was the sister of 16-year-old Kimani Gray, who police said pointed a loaded pistol at two officers before they gunned him down Saturday.

Mahnefah Gray and most of the others were charged with disorderly conduct.

“I was standing at the corner, on the sidewalk, and the cop said, ‘You can’t stand there.’ said Tyreck Strachan, 13, after being released from the 67th Precinct station house.

“I said, ‘I’m on the sidewalk.’ He started hitting me with a stick.”

Tension mounted after a planned 7 p.m. vigil for Gray. The teen’s parents did not show up as expected, and within a few hours, as many as 200 furious protesters started roaming the neighborhood, as they did Monday night.

They marched down Church Ave. toward the station house, where they splintered off and ran amok. The officer who was hit was not seriously injured.

Last night’s trouble came after officials revealed yesterday that Kimani, a reputed Bloods gang member, had been hit with seven bullets.

An autopsy showed he had been shot in the front and back — indicating that he was facing officers when the shooting began, a law-enforcement source said.